Optimal Mix Algorithms with Existing Units

In this paper we develop a series of algorithms to find the optimal mix of units in a given target year for an all-thermal power system with existing units. Initiating the procedure by finding the optimal mix solution for the new units only, the algorithm then proceed to find the loading points of the existing units by solving one dimensional auxiliary problems. The algorithms are developed for both the case where no constraint is imposed on the utilization of the existing units´ capacities and the case where all existing units are enforced to participate in the optimal mix solution at their rated capacities.